(a) Field of the Invention
The present invention relates to a touch switch for controlling accessory equipment of a vehicle according to a change in electrostatic capacitance caused when touched by a user.
(b) Description of the Prior Art(s)
Generally, an inner-door panel of a vehicle has a door pocket in which items such as maps or the like are stored by a vehicle occupant. It is, however, often difficult to retrieve a desired item from such a door pocket because usually light does not fully reach into the door pocket interior. As one attempt to provide a solution, door pockets provided with a lamp which can be turned on and off with a touch switch are sometimes provides. FIG. 8 shows the structure of such a door pocket according to a related technology.
In this example, the door pocket is comprised of mutually opposed side walls 10A and 10B, a main wall 10C which is connected to the side walls 10A and 10B to form a U-shaped wall, and a bottom plate 10D which makes the bottom of the door pocket. The door pocket is fitted to an interior panel 12 such that an opening on the opposite side of the main wall 10C comes into contact with the door interior panel 12. A lamp 14 is attached to the inside surface of the side wall 10A of the door pocket. A touch plate 16 which configures a vehicle accessory touch switch is fixed to the inside surface of the main wall 10C of the door pocket. When the touch plate 16 is touched by a human hand to turn on the vehicle accessory touch switch, the lamp 14 is supplied with power and turned on.
By configuring as described above, the lamp 14 can be turned on when the vehicle occupant inserts his or her hand into the door pocket and touches the touch plate 16. Thus, the occupant can easily retrieve an item stored in the door pocket.
FIG. 9 shows a structure of a vehicle accessory touch switch 18 applied to a door pocket. The touch plate 16 is formed of a dielectric material such as a synthetic resin or the like. A sensor conductor plate 20 is bonded to one surface of the touch plate 16 and connected to a capacitance measurement/control unit 24. The capacitance measurement/control unit 24 is connected to a ground conductor 26 having electric potential as reference.
A switch 28 is controlled to be in ON or OFF state by the capacitance measurement/control unit 24. One of the terminals of the switch 28 is connected to a negative terminal of a battery 30. The other terminal of the switch 28 is connected to one of terminals of the lamp 14. The other terminal of the lamp 14 is connected to the positive terminal of the battery 30.
The capacitance measurement/control unit 24 measures the electrostatic capacitance between the sensor conductor plate 20 and the ground conductor 26 (hereinafter, the electrostatic capacitance or capacity between the conductor plate and the ground conductor 26 is simply referred to as “the capacitance to ground”) and controls the switch 28 if the measured value has a change which exceeds a prescribed control judgment value.
According to the above-described configuration, the capacitance to ground of the sensor conductor plate 20 can be changed when a surface of the touch plate 16, which is opposite to a surface to which the sensor conductor plate 20 is bonded, is touched with a human hand having electrostatic capacity with respect to the ground conductor 26. Thus, lighting of the lamp 14 can be controlled by touching the touch plate 16 with a hand.
A related technology of the present invention is described in JP-A 2006-196395.
However, because the capacitance to ground of the sensor conductor plate 20 is variable depending on a change in humidity or the like of air around the vehicle accessory touch switch 18, the vehicle accessory touch switch 18 may not function properly when the capacitance to ground is varied due to a change in atmospheric conditions. Also, a noise voltage may be induced in the conductor plate 20 by an unnecessary electromagnetic wave generated by other electric equipment, and an error occurs in the electrostatic capacitance measured by the capacitance measurement/control unit 24, possibly causing a malfunction of the vehicle accessory touch switch 18.
The present invention was achieved in view of the above-noted problems. Specifically, the present invention provides a touch switch for controlling accessory equipment of a vehicle that a malfunction which is caused by a factor due to changes in the environment such as a change of atmospheric conditions, receipt of an unrelated electromagnetic impulse, or the like can be avoided.